The invention relates to a piecing process of an open-end friction spinning unit of the type including friction surface members for forming yarn in a yarn-forming zone. The friction surface members are moved and interrupted by a friction surface driving device.
In a known piecing process of this type (DE-OS No. 33 21 234), the drive of the rollers is interrupted when the yarn end to be pieced is inserted into the yarn-forming zone formed in the wedge-shaped gap. During this time, the suction device is also switched off. During the piecing, the suction device is first switched on again, and then, while the piecing takes place, the drive of the rollers is restarted. However, it was found that during the restarting of the rollers for a piecing process, yarn breakages frequently occur again immediately.
An object of the invention is to provide a process and an arrangement in which the rate of success of the piecing can be increased.
This object is achieved by providing a yarn orientation device which orients the yarn during a piecing process. The piecing process includes placing the yarn end into the yarn-forming zone when the friction surface members are stopped. When the friction surface members are started, the yarn orientation device prevents the yarn end from being pulled too far into the yarn-forming zone.
Further advantageous features of a preferred embodiment include friction rollers operating as the friction surface device, and the rollers are started in such a way that the roller rotating out of the yarn-forming zone starts at the same time as or earlier than the roller rotating into the yarn-forming zone.
In another advantageous feature of a preferred embodiment of the invention, a suction device is provided for holding forming yarn in the yarn-forming zone. In this embodiment, the suction device is switched off when the yarn to be pieced is inserted, and the suction device is switched on after the restarting of the drive of the rollers.
In other advantageous features of a preferred embodiment of the invention, the suction device is also switched off when the yarn end to be pieced is inserted. The drive of the rollers is designed in such a way that the roller rotating out of the yarn-forming zone starts at the same time as or earlier than the roller rotating into the yarn-forming zone, and the suction device is switched on after the restarting of the drive of the rollers.
All these features are based on the recognition that a cause of an unsuccessful piecing is that during the starting of the rollers, the roller rotating into wedge-shaped gap sometimes starts first, and the yarn end to be pieced is pulled too deeply into the wedge-shaped gap, is overtwisted and torn off. This can be avoided according to the advantageous features discussed above, by assuring that during the piecing, the yarn end does not enter too deeply into the wedge-shaped gap. This can be achieved either by assuring that the roller rotating out of the wedge-shaped gap does not start in a delayed way or assuring that the suction pull is not in effect during the piecing. The safest way is a combination of these two measures. In view of the fact that the rollers usually run up to the operating speed in a time period of about one second, it is sufficient that the earlier starting of the roller rotating out of the wedge-shaped gap and/or the delayed switching-on of the suction pull of the suction device takes place in fractions of a second.
In other advantageous features of a preferred embodiment of the invention, for carrying out the process a driving belt is provided that drives the rollers. The driving belt can be lifted off for interrupting the operation and can be placed back for restoring it. The rollers are arranged relative to the driving belt in such a way, and/or the driving belt is guided by guiding elements in such a way that when the driving belt is placed back onto the rollers, the driving belt is first placed on the roller rotating out of the yarn-forming zone. Thus it is reliably achieved that the desired earlier starting of the roller rotating out of the yarn-forming zone takes place.
In other advantageous features of a preferred embodiment of the invention, an arrangement for carrying-out the process is provided that includes a device for the lifting off and placing back of a driving belt driving the rollers which is coupled with a device for the switching-on and switching-off of the suction device in such a way that the switching-back-on of the suction device is delayed with respect to the placing of the driving belt back onto the rollers. In both cases, it is assured by a constructive development that the desired starting conditions occur automatically without special measures taken by an operator or by an automatic servicing arrangement.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.